Joju,
Who ever suggested chromium trioxide to you as a stock stain is either very foolish, very ignorant or really *#)*^~ at you!
Chromium salts, including chromium trioxide, are generally very toxic. Chromium attacks the central nervous system and produces symptoms similar to multiple sclerosis. The damage is permanent - you don't get better! Using the stuff exposes you to chromium toxicosis.
Chromium salts all progress to one of several chromium oxides when exposed to air. All of the chromium oxides arebrown to green in color. Most wood stained with chromium trioxide will eventually turn a nauseating green color. This is not generally considered a desired result. it is up to you.
With such a long, successful history of the use of either acid/iron stains or commercially available pigment stains there is to my mind absolutely no justification for using chromium compounds - NONE!
This is serious stuff! If you just ruin and expensive piece of wood you are getting off lucky!
Best Regards,
JMC